The present invention relates to deformable rotary screens.
More particularly, the invention relates to deformable rotary screens of cylindrical configuration.
Still more particularly, the invention relates to deformable rotary cylindrical printing screens of the kind used, for example, in screen printing machines.
Printing screens of this kind are known and are quite widely used. They operate either continuously or discontinuously, being rotated relative to a workpiece to which they apply either a uniform color coating or which they print with a pattern having one or more colors. In the intermediate phases the screen is lifted off the workpiece. A great variety of different workpieces can be treated with such screens, and a particularly well-suited field has been found to be the printing (the term will be used herein for both patterned and non-patterned application of a flowable medium, such as for example printing ink, to a workpiece) of fibrous workpieces, such as smooth-surfaced or napped textiles, fibrous slivers and non-wovens. However, these screens can also be successfully used to print such workpieces as paper, synthetic plastic foils, and the like. The medium used for printing may be liquid ink, ink in form of paste, or a foamed treating medium. The medium need by no means be only a coloring agent, or to contain such a coloring agent; in may, instead, be or contain other agents such as are used for surface-coating the workpiece, or to fire-proof it, moth-proof it, enhance its "hand", impart gloss, etch the surface, or the like.
A problem encountered in the prior art, especially when relatively viscous media are to be applied to workpieces via screens of the type here under discussion, is that the weight of the medium sump which must be maintained within the confines of the screen (and which rests on the inner surface thereof, just ahead of the applicator device which forces medium from the sump through the screen and onto the workpiece), tends to deform the screen so that it loses its cylindrical roundness. This is undesirable for two reasons: it causes the screen to flex every time it performs a revolution and thus fatigues the screen material (usually metal) and it results in an inferior printing job due to uneven application of the medium to the workpiece. Further improvements in connection with the operation of such cylindrical screens are therefore clearly desirable but have, to date, not been forthcoming.